In agricultural seeding operations agricultural materials in liquid or dry granular form are spread over the surface of a field using an agricultural applicator. Liquid applicators are most commonly referred to as sprayers, while dry granular applicators are referred to as granular applicators. Typically such applicators comprise a central container carried on a frame supported on wheels, and applicator booms extending a considerable distance to each side so that a significant width can be covered in each pass. Applicator widths of 120 feet or more are common. The agricultural materials are carried from the container along the booms by a pump, air blast, or the like as is well known in the art.
Similar applicators are used in industrial and commercial applications for ground maintenance or treatment.
In conventional applicators traveling typically at speeds of 5-8 miles per hour (mph), the booms are generally supported by one or more gauge wheels such that the boom moves up and down on the gauge wheels to follow the ground. The gauge wheels prevent the boom from contacting the ground, and maintain the proper boom height to maintain even application as the terrain varies. The operation of such a conventional boom with gauge wheels to allow the boom to follow the ground is disclosed in U.S. Pat. No. 4,650,124 to Connaughty et al. In some applicators, a skid shoe or the like is used instead of a wheel to act as the gauge member.
High speed applicators have recently become very popular, as they reduce the application time considerably. These are designed to operate at relatively high speeds of 15 to 20 mph. Such high speed applicators use a “suspended boom” arrangement wherein the boom extends to the side supported only at the inner end, with no gauge members. Gauge members have not been commonly used on high speed applicators. The booms can be quite heavy and so considerable weight must be carried by the gauge members. This weight on the gauge members creates a significant rearward force, especially in soft soil. As applicator speed increases, the rearward force exerted by resistance of the gauge members traveling over the ground increases as well. The boom must be strong enough to overcome this resistance, requiring increased weight, and compounding the problem.
With a suspended boom, there is no resistance from gauge members. The disadvantage is that the height of the boom is not controlled except at its inside end where it is attached to the applicator frame. The outer end of the boom can contact the ground in uneven terrain, and as well the proper boom height is not maintained nearly as well as when gauge members are used.
To address this problem, it is common to provide individually controllable hydraulic cylinders, commonly referred to as “shoulder cylinders”, attached between the frame and each boom such that each boom can be pivoted upward about its inner end, where it is pivotally attached to the frame. In this way the operator can control the height of the outer end of each boom independently, and maintain an appropriate boom height while going through ditches and similar terrain variations.
Considerable prior art has been addressed to alleviating the problems associated with suspended booms. For example, U.S. Pat. No. 4,427,154 to Mercil, U.S. Pat. No. 4,598,830 to Fletcher, U.S. Pat. No. 4,643,358 to Jackson, U.S. Pat. No. 5,348,226 to Heiniger et al., and U.S. Pat. No. 6,234,407 to Knight et al. disclose variations directed to improved performance of suspended boom applicators.
High speed applicators are commonly used in high standing crops at distances of four or more feet above the ground. At these higher boom heights, the problem of the outer end of the boom hitting the ground is much reduced, and the proper boom height is much more variable. Thus such high speed applicators with suspended booms are well suited for operations in more mature crops at increased boom heights, but are less effective and problematic at lower boom heights.